Systems and methods for detecting change in species in an environment

ABSTRACT

The present disclosure provides embodiments for diodes, devices, and methods for polar vapor sensing. One embodiment of a diode includes a first electrode to which an electric field is applied; a second electrode to which the electric field is applied; and a vapor gap region between the first electrode and the second electrode. A total capacitance measured between the first electrode and the second electrode varies based on presence of a polar vapor species on at least a portion of an electrode surface of at least one of the first electrode and the second electrode.

FIELD OF THE INVENTION

The disclosure relates generally to semiconductor processes and devices,and more particularly to methods for forming semiconductor devicescapable of detecting changes in species in vapor or particle form in anenvironment.

BACKGROUND OF THE INVENTION

There has been significant interest and research in the field of solidstate photoelectric and biochemical vapor and particle detectors. Indetecting various species in vapor and particle form, various relativelycomplex and high cost solutions have been developed, but are unsuitablefor low cost, portable devices operating at room temperature.

A PIN diode is a semiconductor diode with a lightly doped intrinsicsemiconductor region in a substrate between a p-type region and ann-type region. For particle detection, when radiation or chargedparticles of sufficient energy impact the intrinsic region, anelectron-hole pair is created that generates current between the p-typeand n-type regions. The p and n-type regions and the intrinsic regionalso have a measurable capacitance. The PIN diode can be used to detectphotons as well as various types of charged particles including alphaparticles and beta particles in a variety of sensors, such as radonsensors, radiation sensors, light sensors, and smoke detectors, amongothers.

One difficulty with using PIN diodes for sensors is the lack ofsensitivity to detect indirectly ionizing neutrons because the impact ofa neutron in the intrinsic region does not directly generate current asneutrons are electrically neutral. Additionally, the usefulness of asensor is often proportional to the sensitivity of the PIN diode. It istherefore desirable to provide PIN diodes with enhanced levels ofsensitivity, and with the ability to detect neutrons and to identifychanges in vapor content in an environment, in addition to, or insteadof, charged particles and photons.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of exampleand are not limited by the accompanying figures, in which likereferences indicate similar elements. Elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale.

FIG. 1 is a block diagram of an embodiment of a vapor sensor system inaccordance with the present invention.

FIG. 2 is a top view of an embodiment of electrodes in the vapor sensorsystem of FIG. 1.

FIG. 3 is an example of a graph of capacitance ratio versus frequency atvarious spacings between the electrodes of FIG. 2.

FIG. 4 is an example of a graph of capacitance versus frequency forwater vapor detection for various water concentrations in a sample, astested by the sensor system of FIG. 1.

FIG. 5 shows an example of a graph of capacitance versus waterconcentration for water vapor detection at various frequencies, astested by the sensor system of FIG. 1.

FIG. 6 is an example of a graph of capacitance versus alcoholconcentration in water, as tested by the sensor system of FIG. 1 at aparticular frequency.

FIG. 7 is an embodiment of another sensor system that can be used todetect acetone even when mixed with ethanol.

FIG. 8 is an example of a graph of capacitance versus acetone/ethanolconcentration, as tested by the sensor system of FIG. 7 at variousfrequencies.

FIG. 9 is a cross-sectional side view of a portion of a PIN diode, at anintermediate stage of manufacture, according to an embodiment of theinvention.

FIG. 10 is a cross-sectional side view of the PIN diode of FIG. 9, at asubsequent stage of manufacture, according to an embodiment of theinvention.

FIG. 11 is a cross-sectional side view of the PIN diode of FIG. 10, at asubsequent stage of manufacture, according to an embodiment of theinvention.

FIG. 12 is a cross-sectional side view of the PIN diode of FIG. 11, at asubsequent stage of manufacture, according to an embodiment of theinvention.

FIG. 13 is a cross-sectional side view of the PIN diode of FIG. 12showing various types of particles impacting nanoclusters and theintrinsic region, according to an embodiment of the invention.

FIG. 14 is block diagram of a sensor system for detecting neutrons,charged particles, and changes in vapor composition in an environmentusing the PIN diode of FIGS. 1 and/or 13, according to an embodiment ofthe invention.

FIG. 15 is a set of graphs showing example test results of the spectralresponse of the PIN diode of FIG. 13 compared to a conventional PINdiode without nanoclusters.

FIG. 16 is a graph of an example of an amplified output of PIN diode ofFIG. 13 upon a 10 meV cold neutron strike.

FIG. 17 shows an example of the output of three variants of PIN diode ofFIG. 13 exposed to X-radiation.

DETAILED DESCRIPTION

Embodiments disclosed herein provide an enhanced PIN diode detector witha silicon nanocluster-based scattering and electrically polarizedprimary interaction top layer (PIL) for vapor, photo particle, and/orionization detection. When operating to detect a change in compositionof a polar or charged vapor, the detector senses capacitance ofelectrodes to which the polar vapor has been attracted by a positive ornegative charge on the electrodes. A change in the level of capacitanceof the sensor system is an indicator of a change in the amount orcomposition of the vapor. Once a change in the capacitance is detected,this information may be provided to a controller so that appropriateaction may be taken. For detecting photo particles or ionization, thenanoclusters are three-dimensional surfaces with high surface areaencapsulated with dielectric that can be included in the sensor systemto serve as physical scattering sites for incoming photon radiation.Compared to two-dimensional scattering sites, the increased surface areaof the three-dimensional nanoclusters enhances absorption of theradiation in the underlying intrinsic region. Additionally, theinteracting nanocluster dipoles in the enhanced PIN diode electric fieldinduces deflection of charged particles such as alpha and beta particlesin to the sensing volume, which further enhances the probability ofdetecting them. Still further, boron (¹⁰B) isotope used as a nanoclusterdopant generates ionizing alpha particles upon interaction with neutronradiation thereby enabling indirect detection of neutrons, which areotherwise hard to detect. The sensor system can be configured to detectchanges in polar vapor and/or particles in an environment, and/or todetect charged and uncharged particles in the environment.

FIG. 1 is a block diagram of an embodiment of a sensor system 100 inaccordance with the present invention that includes semiconductorsubstrate 102, n-type doped region 103 and p-type doped region 104 insubstrate 102, electrode 106 coupled in ohmic contact with n-type dopedregion 103, electrode 108 coupled in ohmic contact with p-type dopedregion 104, a layer of insulating material 110 grown or deposited onsubstrate 102 between electrodes 106 and 108, an alternating voltagesource 112, and total or equivalent capacitance meter 114. Voltagesource 112 and capacitance meter 114 are coupled in series with oneanother between electrode 106 and electrode 108. A first terminal ofvoltage source 112 is coupled to electrode 106, a second terminal ofvoltage source 112 is coupled to a first terminal of capacitance meter114, and a second terminal of capacitance meter 114 is coupled toelectrode 108. Insulating material 110 can be any suitable oxide ordielectric material that electrically insulates electrode 106 fromelectrode 108. Electrodes 106, 108 may be formed on substrate 102 bypatterned etching a layer of aluminum or other electrically conductivematerial or other suitable technique for forming electrodes 106, 108.N-type doped region 103 may be implanted with phosphorous or othersuitable material to have a higher concentration of electrons thansubstrate 102 and p-type doped region 104. P-type doped region 104 maybe implanted with boron or other suitable material to have a higherconcentration of holes than substrate 102 and n-type doped region 103.Sensor system 100 can operate at room temperature, but is also capableof operating at other ambient temperatures.

When alternating voltage is applied, an electric field around electrodes106, 108 attracts charged vapor species that are capable of movingthrough the ambient environment in the proximity of electrodes 106, 108.For example, a polar molecule like water will have its positivelycharged hydrogen atoms attracted to and oriented towards a negativeelectrode and negatively charged oxygen atom oriented away from thenegative electrode. An alternating voltage being applied between the twoelectrodes, 106, 108 will cause the water molecules to rotate inresponse to the changing electrode polarities at each of the twoelectrodes, 106, 108. This polarization phenomenon manifests itself asan electrode capacitance change which in turn alters the overallequivalent circuit capacitance of sensor system 100 which can bemeasured by total or equivalent capacitance meter (CEQ Meter) 114.

CEQ meter 114 is a logic circuit configured to measure the totalcapacitance of sensor system 100 including capacitance of electrodes106, 108 (shown as CEN and CEP, respectively), substrate 102 (shown asCS), and vapor gap 120 (shown as CGAP) between electrodes 106, 108. Whenpower of a known current (I) and voltage (V) is applied by alternatingvoltage source 112, the total or equivalent capacitance (CEQ) of sensorsystem 100 can be determined over time (t) using the relationshipCEQ=I(t)/(dV/dt). As the number of polar molecules adsorbed onelectrodes 106, 108 changes, an electric double layer 116, 118 forms onelectrodes 106, 108, causing a corresponding change in overallcapacitance of sensor system 100 to be detected. Accordingly, sensorsystem 114 is able to detect when a change in the vapor composition orconcentration of the ambient environment occurs. A signal indicating thecapacitance of sensor system 100 from CEQ meter 114 can be provided to acontroller or other logic circuit (not shown) so that any appropriateaction may be taken.

FIG. 2 is a top view of an embodiment of electrodes 106, 108 in thesensor system 100 of FIG. 1 in which electrodes 106, 108 each include anumber of fingers 204, 206 alternatingly interlaced, or interdigitated,with one another. Any electrodes 106, 108 can include any suitablenumber of fingers 204, 206, for example, fifty or more fingers 204, 206each. One end of each finger 204, 206 is attached perpendicular to arespective linear stem portion 208, 210. The other end of each finger204, 206 extends toward but does not contact the stem portion 208, 210of the other electrode 106, 108. The spacing (S) between fingers 204,206 is selected to provide ample room for the vapor molecules or species202 of interest to collect on the electrode 106, 108 to which thepolar/charged molecule or specie is electrically attracted. The numberof fingers 204, 206 can be chosen based on the amount of space availablefor sensor system 100 and the spacing S between fingers 204, 206. In oneembodiment, fingers 204, 206 have a length of 1214 microns. The width ofstem 208, 210 may vary based on spacing S. For example, width stem 208,210 may vary from 454 microns at a spacing pitch of 0.5 microns to 804microns at a spacing pitch of 4 microns. Other suitable values forspacing, length and width of fingers 204, 206, and stem, 208, 210 can beused.

FIG. 3 is an example of a graph 300 of capacitance ratio versusfrequency at various spacing S between fingers 204, 206 of electrodes106, 108 of FIG. 2. Capacitance ratio was derived by dividing themeasured capacitance at any given frequency by its value at acapacitance of 1 MHz. At high frequencies approaching 1 MHz, the polarmolecules of interest cannot rotate to keep up with the rapidly changingelectric field and therefore the polarization capacitance contributionto the overall measured capacitance decreases and plateaus out to anelectrode pitch independent constant low value. Therefore, thecapacitance ratio can be used as a normalized value to quantifypolarization effects as a function of electrode pitch. The tests forgraph 300 were conducted in an ambient environment with the sameconcentration of vapor molecules. In graph 300, higher capacitance ratioindicates a greater number of vapor molecules collected on electrodes106, 108 and/or enhanced polarization at lower frequencies. Fourdifferent values for spacing S were used, including 4, 2, 1 and 0.5microns resulting in four respective traces 302, 306, 308, 304. Testswere conducted at frequencies of alternating voltage 112 (FIG. 1)ranging from 500 Hz to 1 MHz and an amplitude of 10 mV. The polar vaporspecies form an electric double layer at the surface of electrodes 106,108 whose capacitance contribution to the overall equivalent capacitanceincreases inversely with measurement frequency and directly with vaporconcentration. Accordingly, low frequency capacitance change can becorrelated to a change in polar vapor concentration as the capacitanceof the solid state PIN diode by itself is independent of measurementfrequency and is unaffected by the vapor medium above it.

The highest capacitance for each trace 302, 304, 306, 308 occurs at thelowest frequency, or 500 Hz, with trace 302 at a normalized capacitanceof above 2, trace 306 at a normalized capacitance just over 1.6, trace308 at a normalized capacitance just under 1.2, and trace 304 at anormalized capacitance just over 1. Traces 302-308 decreaseasymptotically from their highest values to a normalized capacitance of1 at a frequency of 1 MHz. From graph 300, polarization of electrodes106, 108 by the vapor molecules 202 in the environment increaseequivalent capacitance of sensor system 100, with increasing capacitanceat lower frequencies. Capacitance enhancement at lower frequencies seenat increasing finger widths is the result of the vapor molecules beingable to more easily collect on electrodes 106, 108 at relaxed pitchconditions to affect electrode polarization behavior.

FIG. 4 is an example of a graph 400 of capacitance versus frequency forwater vapor detection for various water concentrations in a sample, astested by sensor system 100 of FIG. 1. During the tests, a low frequencydielectric spectroscopic technique was used to discriminate betweenethanol blended gasoline fuel and diesel fuel that included exploitingthe difference in dielectric constant between the two fuels. Traces 402and 404 show the capacitance in sensor system 100 over frequencies ofalternating voltage 112 ranging from 30 Hz to 1 kHz. The equivalentcapacitance of system 100 for diesel fuel as shown by trace 402 isapproximately 153 picoFarads (pF) at 30 Hz. Trace 402 decreasesasymptotically to a capacitance of approximately 134 pF at a frequencyof 1 kHz. The equivalent capacitance of system 100 for ethanol blendedgasoline fuel as shown by trace 404 is just above 223 picoFarads (pF) at30 Hz. Trace 404 decreases asymptotically to a capacitance ofapproximately 146 pF at a frequency of 1 kHz. Adding ethanol to gasolineenables electrical discrimination between the two fuels since thedielectric constant of gasoline and diesel are about 2 while ethanol hasa dielectric constant of 24.6 and water has a dielectric constant of80.4.

Additionally, the same low frequency dielectric spectroscopic techniquewas used to quantify water contamination levels leading up to phaseseparation in a commercial ethanol-gasoline blend containing up to 10%ethanol. Traces 406, 407, 408, 410 show the capacitance in sensor system100 over frequencies of alternating voltage 112 ranging from 30 Hz to 1kHz for various combinations of water contamination in ethanol blendedgasoline fuel. Generally, the higher the level of water contamination inthe fuel blend, the higher the equivalent capacitance of sensor system100. In the example shown in FIG. 4, the equivalent capacitance ofsystem 100 for 625 (parts per million) water addition in ethanol blendedgasoline fuel as shown by trace 406 is approximately 333 picoFarads (pF)at 30 Hz. Trace 406 decreases asymptotically to a capacitance ofapproximately 176 pF at a frequency of 1 kHz.

The equivalent capacitance of system 100 for 1250 (parts per million)water addition in ethanol blended gasoline fuel as shown by trace 407 isapproximately 510 picoFarads (pF) at 30 Hz. Trace 407 decreasesasymptotically to a capacitance of approximately 202 pF at a frequencyof 1 kHz.

The equivalent capacitance of system 100 for 1838 (parts per million)water addition in ethanol blended gasoline fuel as shown by trace 408 isapproximately 679 picoFarads (pF) at 30 Hz. Trace 408 decreasesasymptotically to a capacitance of approximately 225 pF at a frequencyof 1 kHz.

The equivalent capacitance of system 100 for 6009 (parts per million)water addition in ethanol blended gasoline fuel as shown by trace 410 isapproximately 1050 picoFarads (pF) at 30 Hz. Trace 410 decreasesasymptotically to a capacitance of approximately 284 pF at a frequencyof 1 kHz.

FIG. 5 is an example of a graph 500 of capacitance versus waterconcentration for water vapor detection at various frequencies, astested by sensor system 100 of FIG. 1. Traces 502, 504, 506, 507, 508show the capacitance in sensor system 100 over water additions rangingfrom 0 ppm to 1838 ppm in ethanol blended gasoline fuel at variousfrequencies. Generally, the lower the frequency of alternating voltage112, the higher the equivalent capacitance of sensor system 100. In theexample shown in FIG. 5, the equivalent capacitance of system 100 at afrequency of 30 Hz in ethanol blended gasoline fuel as shown by trace502 increases from approximately 223 picoFarads (pF) at a water additionof 0 ppm to approximately 679 pF at a water concentration of 1838 ppm.

The equivalent capacitance of system 100 at a frequency of 100 Hz inethanol blended gasoline fuel as shown by trace 504 increases fromapproximately 186 picoFarads (pF) at a water addition of 0 ppm toapproximately 424 pF at a water concentration of 1838 ppm.

The equivalent capacitance of system 100 at a frequency of 200 Hz inethanol blended gasoline fuel as shown by trace 506 increases fromapproximately 174 picoFarads (pF) at a water addition of 0 ppm toapproximately 337 pF at a water concentration of 1838 ppm.

The equivalent capacitance of system 100 at a frequency of 400 Hz inethanol blended gasoline fuel as shown by trace 507 increases fromapproximately 160 picoFarads (pF) at a water addition of 0 ppm toapproximately 275 pF at a water concentration of 1838 ppm.

The equivalent capacitance of system 100 at a frequency of 800 Hz inethanol blended gasoline fuel as shown by trace 508 increases fromapproximately 150 picoFarads (pF) at a water addition of 0 ppm toapproximately 234 pF at a water concentration of 1838 ppm.

The ability to detect differences in fuel blends, as well as watercontamination, could potentially be used both to achieve feed-forwardcontrol of a flex-fuel engine over a range of ethanol content levels aswell as detecting above nominal water contamination levels in the fuel.If water contamination or improper fuel blend is detected, pre-emptiveaction could be taken before phase separation occurs. FIGS. 4 and 5 alsohighlight the point that equivalent capacitance of sensor system 100,and therefore detection rates, increase at lower alternating voltagefrequencies.

FIG. 6 is an example of a graph 600 of capacitance versus alcoholconcentration in water, as tested by the sensor system of FIG. 1 at afrequency of 200 Hz. Sensor system 100 has remarkable sensitivity to lowlevels of moisture in solvent vapor such as isopropyl alcohol (IPA), asquantified by its capacitance change versus water content in trace 602.The equivalent capacitance of system 100 at a frequency of 200 Hz asshown by trace 602 decreases from approximately 3081 pF at an IPAconcentration of 80% to approximately 2707 pF at an IPA concentration of90%, approximately 1035 pF at an IPA concentration of 98%, andapproximately 362 pF at an IPA concentration of 100%. This behavior canbe used to detect trace moisture contamination of solvents in storagebefore the solvent is used. In addition, sensor system 100 can be usedto monitor IPA-based semiconductor endpoint drying processes where thevapor-liquid equilibrium conforms to Raoult's law to insure the partsare completely dry, among other uses.

Dielectric spectroscopic behavior of acetone and ethanol are quitesimilar. Therefore, sensor system 100 alone cannot be used todistinguish and negate the interfering effects of ethanol and humidityduring sensitive acetone concentration measurements. Such a test may beencountered when analyzing the breath of a person with high bloodglucose levels who is also suspected of being intoxicated with alcohol.The acetone present in the breath of a person with high blood sugarwould interfere with detection of ethanol derived from consumingalcoholic beverages. To overcome the limitations of sensor system 100 inthis situation, an embodiment of sensor system 700 is shown in FIG. 7that can be used to detect acetone even when mixed with ethanol.

Sensor system 700 includes sensor system 100 in a housing or enclosure706 and a selectively reactive source 704 of, for example, ultraviolet C(UVC) radiation 704 with a wavelength ranging from 280 to 100nanometers. UVC radiation source 704 is oriented to transmit light toirradiate the vapor sample to be measured by sensor system 100. Theozone produced by the UVC radiation source 704 reacts with the acetonein housing 706, forming carbon dioxide, water and oxygen. Photochemicaltransitions of common interfering ethanol and water molecules occur atmuch lower UVC wavelengths so the selective oxidation of acetone usingUVC radiation can be used to determine the polarization capacitancecontribution from the acetone component and hence its originalconcentration in the vapor phase. Additionally, the double bond of theacetone carbonyl group is more reactive than the single bonds inethanol, so purely from an ozone reactivity perspective, ozone is morereactive with acetone than with ethanol, also enabling chemicalselectivity.

During operation, the capacitance of an initial breath sample can bemeasured without radiation from UVC radiation source 704 at lowfrequency of alternating voltage 112. UVC radiation source 704 is thenactivated and UVC light transmitted for a predetermined amount of timeto oxidize the acetone in the sample. UVC radiation source 704 is thendeactivated to terminate the acetone oxidation reaction. The capacitanceof the oxidized breath sample is then measured at the same low frequencyas the initial breath sample, without UVC radiation. At any givenfrequency, the difference in capacitance between the initial sample andthe oxidized sample can be correlated to the original acetoneconcentration in the sample.

Note that alternative or more selectively reactive sources 704 can beused in sensor system 700 in addition to, or instead of, UVC radiationsource, to enable sensor system 700 to discriminate between two or moredifferent compounds in a vapor sample.

FIG. 8 is an example of a graph 800 of capacitance versusacetone/ethanol concentration, as tested by the sensor system of FIG. 7at various frequencies. Traces 802, 804, 806, 808, 810 show examples ofthe difference in capacitance in sensor system 700 over acetone orethanol concentrations ranging from 0 percent to 50 percent in water atvarious frequencies of alternating voltage 112. The differentialcapacitance of system 700 at a frequency of 100 Hz as shown by trace 802increases linearly from approximately 42 picoFarads (pF) at an acetoneconcentration of 12.5 percent to approximately 152 pF at an acetoneconcentration of 50 percent.

The differential capacitance of system 700 at a frequency of 30 Hz asshown by trace 804 increases linearly from approximately 71 picoFarads(pF) at an acetone concentration of 12.5 percent to approximately 260 pFat an acetone concentration of 50 percent.

The differential capacitance of system 700 at a frequency of 200 Hz asshown by trace 806 increases linearly from approximately 20 picoFarads(pF) at an acetone concentration of 12.5 percent to approximately 94 pFat an acetone concentration of 50 percent.

The differential capacitance of system 700 at a frequency of 400 Hz asshown by trace 808 increases linearly from approximately 9 picoFarads(pF) at an acetone concentration of 12.5 percent to approximately 54 pFat an acetone concentration of 50 percent.

The differential capacitance of system 700 at a frequency of 30 Hz asshown by trace 810 is less than 30 pF for ethanol concentrations rangingfrom 0 to 50 percent.

Acetone has a dielectric constant of 20.7. Upon 3 minutes of ozoneexposure, approximately 45% of the original volume of the acetone islost to gaseous carbon dioxide and oxygen formation, both of which havea dielectric constant close to 1. This decomposition leads to a netreduction in the dielectric constant of the vapor phase in proportion tothe original acetone concentration. In the tests represented by theresults in graph 800, two capacitance measurements are taken, one of theinitial vapor phase and second of the vapor after UV exposure. Thedifference between the two capacitance measurements is proportional tothe original acetone content in the sample. The relationship betweendifferential capacitance and acetone concentration is very linear. Also,an inverse relationship is exhibited between measurement sensitivity andalternating voltage frequency. The reactivity of ozone with ethanolunder similar conditions however does not lead to a significant changein vapor phase dielectric constant and hence the observed selectivity.This is explained by (a) reduced volumetric loss of ethanol from 3 minozone exposure of 15% relative to 45% for acetone, suggesting onlypartial oxidation to CO₂ per the reaction: C₂H₅OH+4O₃→2CO₂+3H₂O+3O₂ and(b) preferential formation of acetaldehyde as the oxidation product witha dielectric constant close to the original ethanol per the reaction:C₂H₅OH+O₃→CH₃CHO+H₂O+O₂.

FIGS. 9-15 illustrate an example of a PIN diode 901 that can be used insensor systems 100 and 700 to combine a polar vapor sensor with aradiation sensor. FIG. 9 is a cross-sectional side view of a portion ofPIN diode 901 at an intermediate stage of manufacture, according to anembodiment of the invention that includes substrate 903 with p-typedoped region (also referred to at P region) 905, n-type doped region(also referred to as N region) 907, intrinsic region 909, and insulating(also called oxide or dielectric) layer 911. P-type doped region 905 andn-type doped region 907 extend from a first major surface of substrate903 to an intermediate level within substrate 903. For example, the pand n-type regions 905, 907 can be defined with boron and phosphorousdopants respectively via chain implantation to a depth of about 1 micronwith a SIMS measured dopant concentration of about 2e18 atoms/cm³.Intrinsic region 909 extends between and under regions 905 and 907.

The substrate 903 can be a semiconductor material or combination ofmaterials such as, for example, polycrystalline silicon, monocrystallinesilicon, amorphous silicon, gallium arsenide, silicon germanium,silicon-on-insulator (SOI), among other semiconductive material(s). Forexample, substrate 903 can be a 200 mm p-type silicon substrate with anintrinsic resistivity of 1000 ohm-cm.

Insulating layer 911 can be formed over substrate 903 using conventionalgrowth or deposition processes. Insulating layer 911 can be, forexample, SiO₂, HfAlO, HfO₂, ONO, SiON, SiN, or other dielectric orinsulative material, including high dielectric constant material such asalumina, titanium dioxide, hafnium dioxide, tantalum dioxide, and thelike. For example, insulating layer 911 can be a thin LPCVD thermalgrown oxide layer with a thickness ranging from 30 to 100 Angstroms orother suitable thickness.

FIG. 10 is a cross-sectional side view of the PIN diode of FIG. 9, at asubsequent stage of manufacture after a semiconductor layer 1001 isdeposited over insulating layer 911. The deposition step can beperformed using chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), epitaxy (EPI) or other methods. In anembodiment, the substrate 903 can be placed in a deposition chamber anda precursor gas flowed into the chamber to form a thin non-contiguoussemiconductor layer 1001 on the insulating layer 911. For example, anamorphous or a polysilicon layer 1001 can be formed by flowing a siliconprecursor gas, such as silane (SiH₄) or disilane (Si₂H₆), for example,using a conventional CVD process. Deposition time will generallydetermine the thickness of the deposited layer 1001. In an embodiment,for example, the height or thickness of the semiconductor layer 1001(e.g., amorphous/polycrystalline silicon) can be about 3-20 nm. Ingeneral, the deposition temperature is not so high as to control thethickness and morphology of the semiconductor (e.g., amorphous silicon)layer 1001.

FIG. 11 is a cross-sectional side view of the PIN diode of FIG. 10, at asubsequent stage of manufacture after which semiconductor layer 1001(e.g., amorphous/polycrystalline silicon) is annealed to formnanoclusters 1101 of desirable shape and density. In an embodiment, theanneal 1103 of an amorphous/polysilicon layer 1001 can be performed inan ambient (e.g., one or more gases) that does not contain oxygen. Forexample, the ambient can be nitrogen, an inert gas (e.g., argon),hydrogen or a combination thereof. By way of example, an anneal 1103 ofamorphous/polysilicon layer 1001 can be performed at a temperature ofabout 600-1000° C., for a time period of about 5-300 seconds in ahydrogen ambient.

Annealing the semiconductor layer 1001 results in the formation of aplurality of individual, discrete nanoclusters 1101 (also callednanoparticles) which are dispersed over the surface of the insulatinglayer 911. The anneal 1103 causes the semiconductor (e.g.,amorphous/polysilicon) layer 1001 to dewet from the insulating layer 911and form nanoclusters 1101 that are physically separated from eachother. In some embodiments, for example, the nanoclusters 1101 can havean average diameter, thickness or height of about 10-30 nm and beseparated or spaced from one another by 10-30 nm. Nanoclusters 1101 aregenerally uniformly distributed over the surface of the insulating layer911, for example, at a density of about 1e11 to 3e11 nanoclusters percm².

In some embodiments, for example, polysilicon nanoclusters 1101 can beLPCVD nucleated at 620 C followed by their coalescence and insitu dopingwith boron in an EPI reactor at 800 C. Boron doping can be accomplishedthrough a diborane decomposition reaction which results in anapproximately 20%-80% natural split co-doping of ¹⁰B and ¹¹B isotopespecies.

FIG. 12 is a cross-sectional side view of the PIN diode of FIG. 11, at asubsequent stage of manufacture, according to an embodiment of theinvention, after insulating layer (also referred to as dielectric oroxide layer) 1201 has been deposited over nanoclusters 1101 and apatterned etch has been performed on insulating layer 911, nanoclusters1101 and insulating layer 1201 in a desired pattern that exposes thesurface of substrate 903 in a first opening over p-type region 905 andin a second opening over n-type region 907. A conventional masking andetching process can be used to etch insulating layer 911, nanoclusters1101 and insulating layer 1201. In some embodiments, the etching can beperformed through a patterned mask such as a photoresist or other typesof patternable material that can be selectively removed. The mask coverssome of insulating layer 1201 and leaves desired areas for openings overregions 905, 907 exposed. The exposed areas over regions 905, 907 canthen be etched, for example, by a conventional dry or wet etch process.

After the openings over regions 905, 907 are formed, a titanium silicidelayer 1203, 1205 or other suitable material for improving ohmic contactwith regions 905, 907 is formed selectively at the bottom of therespective openings. A layer of titanium nitride 1207, 1209 or othersuitable barrier layer is then deposited over titanium silicide layers1203, 1205, exposed sidewalls of the openings, and overlapping the topedge of insulating layer 1201 adjacent the openings. The titaniumnitride layers 1207, 1209 or other material enables electrical contactto the regions 905, 907 while acting as a diffusion barrier between theunderlying titanium silicide layers 1203, 1205 and metallization to beplaced above titanium nitride layers 1207, 1209.

Electrodes (also referred to as ohmic contacts) 1211, 1213 are thenformed in, above, and slightly overlapping the openings over regions905, 907. Electrodes 1211, 1213 can be made of, for example, a patternedlayer of aluminum, or other suitable conductive material. The thicknessof electrodes 1211, 1213 is typically about 500 nm to several micronsdepending on the application. Electrodes 1211, 1213 can be patterned andetched by using conventional photolithographic processing (e.g., by dryetching) with a mask (not shown). The combination of electrode 1211,metallization layer 1207, silicide layer 1203 and p-type region 905 isreferred to herein as p-terminal 1200 of PIN diode 901. The combinationof electrode 1213, metallization layer 1209, silicide layer 1205, andn-type region 907 is referred to herein as n-terminal 1202 of PIN diode901. The combination of insulating layers 1201, 911, nanoclusters 1101and intrinsic region 909 is referred to herein as detection region 1204of PIN diode 901.

In some embodiments, for example, nanoclusters 1101 can be encapsulatedwith a 100-200 nm plasma enhanced chemical vapor deposition undopedsilicon glass (USG) cap layer, shown as insulative layer 1201, beforebeing lithographically patterned to access the regions 905, 907 forsubsequent contact formation. Once open, regions 905, 907 can beselectively silicided with titanium or titanium compound via RTP using a12 second 685 C anneal resulting in titanium silicide formation.Subsequent metallization with titanium nitride metallization layers1207, 1209 can include blanket deposition of a 250 A titanium nitridewith 600 nm aluminum copper alloy (0.5% Cu) PVD stack. A chlorine-basedendpointed reactive ion etch process can be used to patternmetallization layers 1207, 1209, 1211, 1213 with the etch tailored toreduce insulating layer 1201 to a thickness of 30-50 nm or lower in theopen area from an original thickness ranging from 100-200 nm. Othersuitable materials, processes, and thicknesses can be used in otherembodiments.

In embodiments where optical isolation is desired, i.e., where detectionof visible photons is not required, optical isolator 1215 can be addedover intrinsic region 909 to block visible photons from reachingintrinsic region 909. Optical isolator 1215 can be made of any suitableopaque material, such as aluminum or other suitable material, with athickness of approximately one micron or other suitable thickness. Inother embodiments where visible photon detection is desired, opticalisolator 1215 will not be included over intrinsic region 909. Opticalisolator 1215 is formed so that respective gaps 1217, 1219 remainbetween optical isolator 1215 and each of electrodes 1211, 1213. Forexample, material for isolator 1215 may be deposited so that thematerial fills the space between electrodes 1211, 1213, and then apatterned etch of the material may be performed to remove materialdirectly adjacent electrodes 1211, 1213 or isolator 1215 could be thesame material as the electrodes 1211, 1213 and be patterned concurrentlyin a single patterning step using conventional lithography and etchsteps.

FIG. 13 is a cross-sectional side view of the PIN diode 901 of FIG. 12with reverse bias voltages on electrodes 1211, 1213, that is, p-typeregion 905 is coupled to a first voltage source through electrode 1211and n-type region 907 is coupled to a second voltage source throughelectrode 1213. PIN diode 901 can be reverse biased with a voltage atthe n-type region 907 of 50 mV, or other suitable voltage while p-typeregion 905 is coupled to ground, for example. Various types of particlesare shown being scattered by nanoclusters 1101 into intrinsic region 909including beta particle 1301, neutron 1303, alpha particle 1307 thatformed when neutron 1303 interacted with the ¹⁰B isotope in nanoclusters1101, photon 1305, and alpha particle 1311.

Dipole charge of nanoclusters 1101 is indicated by “+” and “−” signsnext to each nanocluster 1101 in the reverse biased PIN diode electricfield. The dipole charge facilitates deflection of charged species suchas alpha particle 1311 and beta particle 1301 into intrinsic region 909,thereby enhancing interaction probability and detection. The magnifiedelectric field at the nanocluster dielectric interface enables enhanceddeflection of charged particles improving probability of detectionwithin the underlying PIN diode 901. In particular, charged particlesare deflected at the electric dipoles of nanoclusters 1101,supplementing physical scattering effects and enhancing the probabilityof interaction within intrinsic region 909. The three-dimensional shapeof nanoclusters 1101 creates a further physical effect where photon 1305scatters off adjacent nanoclusters 1101 to enhance absorption of photon1305 into intrinsic region 909. Further, the ¹⁰B doping of nanoclusters1101 interacts with neutrons 1303 to generate alpha particle 1307,allowing neutron strikes to be detected with PIN diode 901. Reducing thethickness of insulating layer 911 can further enhance the sensitivity ofPIN diode 901 to photons due to reduced light attenuation in insulatinglayer 911. For example, a PIN diode 901 with an insulating layer 911having a thickness of 45 Angstroms exhibited greater sensitivity tovisible photons 1305 compared to an insulating layer 911 having athickness of 145 Angstroms.

In some embodiments, intrinsic region 909 may be oriented differentlywith respect to p-terminal 1200 and n-terminal 1202 than shown in FIGS.12 and 13. Further, nanoclusters 1101 and insulating layers 1201, 911may be positioned in any suitable orientation and location in whichinteraction between particles and intrinsic region 909 can be enhancedby the presence of nanoclusters 1101.

As used herein, the term “radiation” encompasses pure energy (no mass)such as photons as well as energetic species with mass such as subatomicalpha and beta particles.

Referring to FIGS. 13 and 14, FIG. 14 is a block diagram of anembodiment of a sensor system 1401 for detecting neutrons 1303 thatincludes both PIN diode 901 of FIG. 13 and PIN diode 1403 coupled tomeasuring circuit 1405 according to an embodiment of the invention.Sensor system 1401 may also be used to detect changes in vaporcomposition, such as described for sensor systems 100 and 700hereinabove. The components of PIN diode 1403 include p-terminal 1409similar to p-terminal 1200 of PIN diode 901, n-terminal 1411 similar ton-terminal 1202 of PIN diode 901, and detection region 1413 similar todetection region 1204 of PIN diode 901 except detection region 1413 doesnot include nanoclusters (not shown) in detection region 1413 or anyother primary interaction layer doped with ¹⁰B isotope. PIN diodes 901,1403 are located close enough to one another that a source of neutronsis likely to impact both PIN diodes 901, 1403.

P-terminals 1200, 1409 and n-terminals 1202, 1411 are independentlyreverse biased to enable measurement in a common sensing environment.Measuring circuit 1405 can supply voltage to bias PIN diodes 901, 1403,and can measure one or more electrical characteristics of PIN diodes901, 1403, such as voltage, current, resistance, capacitance, amongothers. Measuring circuit 1405 can include any suitable measuringdevices, such as a charge sensitive amplifier, oscilloscope, and/orcomparator, etc.

An output of measuring circuit 1405 can indicate the difference in ameasured electrical characteristic of PIN diodes 901, 1403. For example,a change in polar vapor composition can be detected by a change incapacitance of pin diode 901 or 1403. As another example, to detectradiation, when neutrons 1303 impact detection region 1204 of PIN diode901, the interaction of neutrons 1303 with the ¹⁰B isotope innanoclusters 1101 will generate alpha particles 1307 and create currentthrough PIN diode 901. Since PIN diode 1403 does not includenanoclusters 1101 doped with the ¹⁰B isotope, PIN diode 1403 will notgenerate alpha particles 1307 from neutrons 1303. The difference incurrent between PIN diode 901 and PIN diode 1403 indicates a neutronstrike since PIN diode 1403 is not capable of generating alpha particles1307 from neutron 1303 and therefore would be insensitive to it. Notethat if both PIN diodes 901, 1403 are struck by alpha particles 1311,alpha particles 1311 will be detected by both PIN diodes 901, 1403rendering the differential current between the two to be essentiallyzero.

Referring to FIGS. 13 and 15, FIG. 15 is a set of graphs 1501, 1503showing test results of the spectral response of PIN diode 901 comparedto a conventional PIN diode without nanoclusters 1101 in the visiblewavelength. Graph 1501 shows photo electric current measured by PINdiode 1403 and graph 1503 shows current measure in PIN diode 901 inresponse to photons in the visible wavelength range including blue,green, yellow and red wavelength regions. Table 1 below shows anenhancement ratio of current in nano-Amperes in PIN diode 901 relativeto current in PIN diode 1403 at each wavelength region shown by graphs1501 and 1503:

TABLE 1 Visible Current in Current in Wavelength PIN Diode PIN DiodeEnhancement Region 901 (nA) 1403 (nA) Ratio Blue −4.6 −2.2 2.1 Green −5−2.1 2.4 Yellow −8.1 −4.1 2.0 Red −4.6 −1.8 2.6

As the results of graphs 1501 and 1503 show, PIN diode 901 is moresensitive to photon detection than PIN diode 1403. The difference insensitivity peaks in the yellow wavelength region with a difference of 4nA between current in PIN diode 901 and PIN diode 1403, but is stillsignificant in the blue, green and red wavelength regions. The enhancedphotoelectric response of PIN diode 901 compared to PIN diode 1403 isdue to scattering of photons by nanoclusters 1101, which effectivelyincreases interaction probability and hence absorption in intrinsicregion 909.

A measurement system for detecting alpha particles can include outputfrom PIN diode 901 being provided to a charge sensitive amplifier modulesuch as the Cremat CR-Z-110 by Cremat Corporation in West Newton, Mass.In one test, the amplified output of the amplifier was input to anoscilloscope. It was demonstrated that an alpha strike from a thoriumsource with a fluence of 70/cm²/sec and peak energy of 4 MeV could bedetected by PIN diode 901 at a signal to noise ratio of 5:1.

FIG. 16 is a graph 1601 of an example of an amplified output of PINdiode 901 of FIG. 13 upon a 10 meV cold neutron strike. Amplification ofthe signal was performed using a Cremat CR-Z-110 charge sensitiveamplifier by Cremat Corporation in West Newton, Mass. The signalelevation shown is from a secondary alpha particle generated uponinteraction of the 10 meV Neutrons with ¹⁰B isotope in nanocluster 1101.This data proves the concept of using ¹⁰B isotope doping of nanoclustersfor detecting thermal neutrons.

In some embodiments, a high atomic number material such as Tungsten canbe coated on the backside of PIN diode 901 to enhance radiationdetection sensitivity via Bremsstrahlung and/or characteristicback-radiation effects. FIG. 17 of graph 1701 shows response of threetypes of PIN diode 901 variants, 1702, 1704 and 1706 to X-radiation.Trace 1702 is the responsivity of a baseline device 901 with nonanoclusters or backside Tungsten. Trace 1704 is the responsivity ofdevice 901 variant with nanoclusters but no backside Tungsten whiletrace 1706 corresponds to a device 901 variant with both nanoclustersand backside Tungsten being present. The variant with both nanoclusters1101 as well as the backside Tungsten coating as shown in trace 1706exhibited the highest responsivity of the three variants. The data ingraph 1701 proves the sensitivity enhancement benefits of thenanoclusters as well as the backside Tungsten concepts.

By now, it should be appreciated that a radiation sensing device hasbeen provided that includes a reverse biased PIN diode 901 with ¹⁰Bnanoclusters 1101 connected in parallel with the intrinsic region 909,and a thin insulative layer 911 between the nanoclusters 1101 andintrinsic region 909. An embodiment in which a high atomic number filmon the backside of substrate 102 to further enhance the sensitivity ofdevice 901 has also been demonstrated. PIN diode 901 thereby is designedto synergistically enhance the capability and versatility ofconventional PIN diodes enabling higher sensitivity and broader range ofphoto and ionization detection at reduced cost.

In some embodiments, a diode includes a first electrode (106) to whichan electric field is applied; a second electrode (108) to which theelectric field is applied; and a vapor gap region (120) between thefirst electrode and the second electrode. A total capacitance (Ceq)measured between the first electrode and the second electrode variesbased on presence of a polar vapor species on at least a portion of anelectrode surface of at least one of the first electrode and the secondelectrode.

In another aspect, molecules of the polar vapor species form an electricdouble layer (116 or 118) at the portion of the electrode surface uponapplication of a low frequency alternating voltage signal (112) betweenthe first and second electrodes. Capacitance (CEN, CEP) due to theelectric double layer increases proportionally with an increase inconcentration of the molecules of the polar vapor species present on theportion of the electrode surface. The total capacitance includes thecapacitance due to the electric double layer.

In another aspect, the low frequency alternating voltage signal can havea frequency of less than 500 Hz.

In another aspect, the first electrode can comprise a first plurality offingers (204 of FIG. 2), the second electrode comprises a secondplurality of fingers (206 of FIG. 2), and the first and second pluralityof fingers form an interdigitated structure.

In another aspect, a spacing (S of FIG. 2) measured between a finger ofthe first plurality of fingers and an adjacent finger of the secondplurality of fingers can be less than or equal to 4 microns.

In another aspect, the first and second electrodes can comprise apassive conductive metal, and the passive conductive metal can compriseone of a group including aluminum and titanium nitride.

In another aspect, the diode can further comprise a first semiconductorregion (103) of a first conductivity type in ohmic contact with thefirst electrode, and a second semiconductor region (104) of a secondconductivity type in ohmic contact with the second electrode. The secondconductivity type is opposite the first conductivity type. An intrinsicsemiconductor region can be included between the first and secondsemiconductor regions, wherein the vapor gap region is above theintrinsic semiconductor region.

In another aspect, the diode can further comprise at least one or moreof: a layer of nanoclusters (1101) located over the intrinsicsemiconductor region, and a layer of non-conductive material (1201)located over the intrinsic semiconductor region.

In other embodiments, a device can comprise a diode that includes afirst electrode (106) to which an electric field is applied, a secondelectrode (108) to which the electric field is applied, and a vapor gapregion (120) between the first electrode and the second electrode. Atotal capacitance (Ceq) measured between the first electrode and thesecond electrode varies based on presence of a first polar vapor specieson at least a portion of an electrode surface of at least one of thefirst electrode and the second electrode. A measuring circuit (114)includes a first terminal electrically coupled to the first electrodeand a second terminal electrically coupled to the second electrode. Themeasuring circuit can be configured to provide a reading of the totalcapacitance measured between the first electrode and the secondelectrode.

In another aspect, molecules of the first polar vapor species can forman electric double layer (116 or 118) at the portion of the electrodesurface upon application of a low frequency alternating voltage signal(112) between the first and second electrodes. A capacitance (CEN, CEP)due to the electric double layer increases proportionally with anincrease in concentration of the molecules of the first polar vaporspecies present on the portion of the electrode surface, and the totalcapacitance includes the capacitance due to the electric double layer.

In another aspect, the device can further comprise a power source (112)having a first terminal electrically coupled to the first electrode anda second terminal electrically coupled to the second electrode. Thepower source can be configured to apply the low frequency alternatingvoltage signal to the first and second electrodes.

In another aspect, the device can further comprise a selectivelyreactive source (704) configured to selectively react with the firstpolar vapor species (e.g., acetone) present within the vapor gap regionand in vicinity of the first and second electrodes to produce one ormore component non-polar vapor species (e.g., CO₂, O₂), wherein a secondpolar vapor species (e.g., water vapor) is also present within the vaporgap region and in vicinity of the first and second electrodes.

In another aspect, the selectively reactive source comprises at leastone or more of: a light source (704) configured to expose the firstpolar vapor species to light of a suitable wavelength capable ofselectively inducing photochemical decomposition of the first polarvapor species, and a chemical source configured to expose the firstpolar vapor species to a chemical compound.

In another aspect, the device can further comprise a logic circuitconfigured to initiate the measurement circuit to provide a firstreading of the total capacitance between the first and secondelectrodes, activate the selectively reactive source to selectivelyreact with the first polar vapor species for a period of time subsequentto initiation of the first reading of the total capacitance, andinitiate the measurement circuit to provide a second reading of thetotal capacitance between the first and second electrodes subsequent toactivation of the selectively reactive source.

In still other embodiments, a method can comprise applying an electricfield to a first electrode (106) and a second electrode (108) of adiode, wherein the first electrode and the second electrode areseparated by a vapor gap region (120) of the diode, and measuring atotal capacitance between the first electrode and the second electrode,wherein the total capacitance varies based on presence of a first polarvapor species on at least a portion of an electrode surface of at leastone of the first electrode and the second electrode.

In another aspect, the method can further comprise introducing a vaporsample to the vapor gap region, wherein the vapor sample comprises thefirst polar vapor species.

In another aspect, the method can further comprise measuring a firstreading of the total capacitance between the first and secondelectrodes, wherein the vapor sample further comprises a second polarvapor species (e.g., water vapor); exposing the vapor sample presentwithin the vapor gap region and in vicinity of the first and secondelectrodes to a selectively reactive source that selectively reacts withthe first polar vapor species (e.g., acetone) to produce one or morecomponent non-polar vapor species (e.g., CO₂, O₂), wherein the exposingis performed for a period of time subsequent to the measuring the firstreading; and measuring a second reading of the total capacitance betweenthe first and second electrodes, wherein the measuring of the secondreading is performed subsequent to the exposing the vapor sample.

In another aspect, the selectively reactive source (704) comprises atleast one or more of: a light source configured to expose the vaporsample to light of a suitable wavelength capable of inducingphotochemical decomposition of the first polar vapor species, and achemical source configured to expose the vapor sample to a chemicalcompound.

In another aspect, a difference between the first reading and the secondreading correlates to a particular concentration of the first polarvapor species (e.g., acetone) present on the portion of the electrodesurface at a time of the first reading.

In another aspect, the first polar vapor species comprises one of agroup including ketones, water vapor, and alcohol.

The terms “top,” “bottom,” “over,” “under,” “overlying,” “underlying,”and the like in the description and in the claims, if any, are used fordescriptive purposes and may, but do not necessarily, describe permanentrelative positions. It is understood that the terms so used may beinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

The terms “a” or “an,” as used herein, are defined as one or more thanone. Also, the use of introductory phrases such as “at least one,” “atleast two,” and “one or more” in the claims should not be construed toimply that the introduction of another claim element by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim element to devices, etc., containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same applies to the use of definite articles.

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of thepresent invention. Any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required or essential feature orelement of any or all of the claims.

What is claimed:
 1. A diode comprising: a first electrode to which anelectric field is applied; a second electrode to which the electricfield is applied; a vapor gap region between the first electrode and thesecond electrode, wherein a total capacitance measured between the firstelectrode and the second electrode varies based on presence of a polarvapor species on at least a portion of an electrode surface of at leastone of the first electrode and the second electrode; a firstsemiconductor region of a first conductivity type in ohmic contact withthe first electrode; a second semiconductor region of a secondconductivity type in ohmic contact with the second electrode, whereinthe second conductivity type is opposite the first conductivity type;and an intrinsic semiconductor region between the first and secondsemiconductor regions, wherein the vapor gap region is above theintrinsic semiconductor region.
 2. The diode of claim 1, whereinmolecules of the polar vapor species form an electric double layer atthe portion of the electrode surface upon application of a low frequencyalternating voltage signal between the first and second electrodes, acapacitance due to the electric double layer increases proportionallywith an increase in concentration of the molecules of the polar vaporspecies present on the portion of the electrode surface, and the totalcapacitance includes the capacitance due to the electric double layer.3. The diode of claim 2, wherein the low frequency alternating voltagesignal has a frequency of less than 500 Hz.
 4. The diode of claim 1,wherein the first electrode comprises a first plurality of fingers, thesecond electrode comprises a second plurality of fingers, and the firstand second plurality of fingers form an interdigitated structure.
 5. Thediode of claim 4, wherein a spacing measured between a finger of thefirst plurality of fingers and an adjacent finger of the secondplurality of fingers is less than 4 microns.
 6. The diode of claim 1,wherein the first and second electrodes comprise a passive conductivemetal, and the passive conductive metal comprises one of a groupincluding aluminum and titanium nitride.
 7. The diode of claim 1,further comprising at least one or more of: a layer of nanoclusterslocated over the intrinsic semiconductor region, and a layer ofnon-conductive material located over the intrinsic semiconductor region.8. A device comprising: a diode, the diode comprising: a first electrodeto which an electric field is applied, a second electrode to which theelectric field is applied, and a vapor gap region between the firstelectrode and the second electrode, wherein a total capacitance measuredbetween the first electrode and the second electrode varies based onpresence of a first polar vapor species on at least a portion of anelectrode surface of at least one of the first electrode and the secondelectrode; a first semiconductor region of a first conductivity type inohmic contact with the first electrode; a second semiconductor region ofa second conductivity type in ohmic contact with the second electrode,wherein the second conductivity type is opposite the first conductivitytype; an intrinsic semiconductor region between the first and secondsemiconductor regions, wherein the vapor gap region is above theintrinsic semiconductor region; and a measuring circuit having a firstterminal electrically coupled to the first electrode and a secondterminal electrically coupled to the second electrode, wherein themeasuring circuit is configured to provide a reading of the totalcapacitance measured between the first electrode and the secondelectrode.
 9. The device of claim 8, wherein molecules of the firstpolar vapor species form an electric double layer at the portion of theelectrode surface upon application of a low frequency alternatingvoltage signal between the first and second electrodes, a capacitancedue to the electric double layer increases proportionally with anincrease in concentration of the molecules of the first polar vaporspecies present on the portion of the electrode surface, and the totalcapacitance includes the capacitance due to the electric double layer.10. The device of claim 9, further comprising a power source having afirst terminal electrically coupled to the first electrode and a secondterminal electrically coupled to the second electrode, wherein the powersource is configured to apply the low frequency alternating voltagesignal to the first and second electrodes.
 11. The device of claim 8,further comprising: a selectively reactive source configured toselectively react with the first polar vapor species present within thevapor gap region and in vicinity of the first and second electrodes toproduce one or more component non-polar vapor species, wherein a secondpolar vapor species is also present within the vapor gap region and invicinity of the first and second electrodes.
 12. The device of claim 11,wherein the selectively reactive source comprises at least one or moreof: a light source configured to expose the first polar vapor species tolight of a suitable wavelength capable of selectively inducingphotochemical decomposition of the first polar vapor species, and achemical source configured to expose the first polar vapor species to achemical compound.
 13. The device of claim 11, further comprising: alogic circuit configured to initiate the measurement circuit to providea first reading of the total capacitance between the first and secondelectrodes, activate the selectively reactive source to selectivelyreact with the first polar vapor species for a period of time subsequentto initiation of the first reading of the total capacitance, andinitiate the measurement circuit to provide a second reading of thetotal capacitance between the first and second electrodes subsequent toactivation of the selectively reactive source.